Sofema Aviation Services (SAS) considers key aspects related to EWIS Design Considerations
Introduction
As aircraft systems continue to evolve, the complexity and safety-critical nature of Electrical Wiring Interconnection Systems (EWIS) demand a robust and harmonised regulatory approach.
- Recognising this, both the Federal Aviation Administration (FAA) and the European Union Aviation Safety Agency (EASA) have issued detailed guidance under FAR/CS-25 Subpart H, supported by FAA Advisory Circulars (ACs) and EASA’s AMC 20-21.
Regulatory & Guidance Frameworks
- FAA FAR 25 Subpart H: EWIS safety regulations applied in U.S. certification.
- EASA CS-25 Subpart H: European Certification Specifications with similar intent and scope.
- FAA ACs (Advisory Circulars): Non-binding, interpretive material supporting compliance with FAR.
- AMC 20-21: Acceptable Means of Compliance offering structured guidance for EWIS development assurance under CS-25.
Integrated Overview: FAA ACs, EASA CS-25 & AMC 20-21
Surface Exposure and Accessibility – FAA: AC 25.1703 | EASA: CS 25.1703 | AMC 20-21 Section 7
Focuses on the identification and mitigation of damage-prone wiring installations. Emphasises separation, protection, and inspection access.
Engineering Actions:
- Perform zonal analysis to assess mechanical risk.
- Design protective routing and separation schemes.
- Address maintainability and inspection access in high-risk zones.
Fuel Tank Wiring and Shielding – FAA: AC 25.1705 / AC 25.981-1C | EASA: CS 25.1705 / CS 25.981 | AMC 20-21 Sections 9 & 11
Addresses prevention of ignition sources in or near fuel systems. Emphasises shielding, segregation, fault tolerance, and installation quality.
Engineering Actions:
- Apply separation distances, robust shielding, and EMI protection.
- Conduct fault hazard analyses and define Failure Conditions.
- Demonstrate compliance through FMEA and zoning risk mitigation.
System Interface Requirements – FAA: AC 25.1707 | EASA: CS 25.1707 | AMC 20-21
Ensures functional and physical compatibility of EWIS components with interfacing systems.
Engineering Actions:
- Validate electrical interface specifications (voltage, current, EMI).
- Verify continuity and grounding across all interfaces.
- Coordinate interface definition with avionics and systems engineers.
Fire Protection in Design – FAA: AC 25.1709 / AC 25.869-1A | EASA: CS 25.1709 / CS 25.869 | AMC 20-21 Sections 8 & 10
Mandates flame resistance and fire-containment capabilities for wiring in fire zones.
Engineering Actions:
- Select fire-resistant insulation materials.
- Implement thermal barriers and install wiring away from flammable zones.
- Document flammability test compliance and survivability criteria.
Electrical Safety and Circuit Protection – FAA: AC 25.1357-1A / AC 25.1362 | EASA: CS 25.1357 / CS 25.1362 | AMC 20-21 Section 5
Provides protection from electrical faults, overcurrents, and fire hazards.
Engineering Actions:
- Incorporate circuit breakers, fuses, and fault-isolating features.
- Use wire sizing, routing, and load protection principles.
- Validate protective device performance under operational conditions.
AMC 20-21 – Development Assurance of EWIS
AMC 20-21 provides overarching guidance for the development assurance of EWIS, emphasising a systematic, risk-based approach. Key expectations include:
- Development Assurance Process (DAP)
>> Align EWIS risk classification with system safety objectives.
>> Establish development processes based on criticality (e.g., Failure Conditions and DAL).
- Configuration and Design Control
>> Maintain traceability of EWIS design decisions.
>> Ensure configuration control from initial design through post-certification changes.
- Installation and Maintenance Considerations
>> Ensure the design supports safe and consistent installation.
>> Plan for ease of maintenance and inspection access over the aircraft lifecycle.
- Verification and Validation
- Apply a combination of analysis, inspection, and testing to demonstrate compliance.
- Use structured documentation to support certifying authority reviews.
Engineering Responsibilities in the EWIS Compliance Context
Achieving EWIS compliance is a multidisciplinary engineering effort, requiring ownership and proactive engagement throughout the aircraft lifecycle.
Core Engineering Responsibilities:
- Risk-Based Design: Identify and mitigate EWIS-specific hazards, including degradation, thermal stress, EMI, and physical damage.
- Interface Management: Ensure compatibility and integrity across all system connections, using grounding and shielding best practices.
- Development Assurance: Apply structured, process-driven design and validation activities aligned with AMC 20-21 expectations.
- Certification Support: Deliver comprehensive compliance data, including FMEA, test reports, and analysis documentation.
- Lifecycle Focus: Plan for maintainability, inspections, and safe integration of upgrades or modifications.
Next Steps
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Sofema Aviation Services Provides Specialised EWIS Training for Design Organisations – Electrical Wiring Interconnection System (EWIS) and FAA-EASA Part 23-25 Certification – 4 Days. For details, please email [email protected].
Tags:
SAS blogs, aircraft systems, EASA CS-25, Federal Aviation Administration (FAA), European Union Aviation Safety Agency (EASA), EWIS Compliance, AMC 20-21 Integration, FAA Advisory Circulars (ACs), FAA FAR 25 Subpart H, EASA CS-25 Subpart H, Electrical Safety, Circuit Protection
